Methodology for implementing enhanced optical lithography for hole patterning in semiconductor fabrication

ABSTRACT

System and method for enhancing optical lithography methodology for hole patterning in semiconductor fabrication are described. In one embodiment, a photolithography system comprises an illumination system for conditioning light from a light source, the illumination system producing a three-pore illumination pattern; a reticle comprising at least a portion of a pattern to be imaged onto a substrate, wherein the three-pore illumination pattern produced by the illumination system is projected through the reticle; and a projection lens disposed between the reticle and the substrate.

BACKGROUND

The fabrication of integrated circuits (“ICs”) involves the performanceof a range of chemical and physical processes on a semiconductorsubstrate. In general, these processes include deposition, patterning,and doping. Fundamental to all of these processes is lithography, bywhich process three-dimensional relief images are formed on a substratefor subsequent transfer of a pattern to the substrate.

Lithography accounts for a large part of the cost of IC fabrication, dueto the large number of lithography steps involved in fabrication. Inaddition, lithography generally presents the primary limitation tofurther advancements in the reduction of feature size and silicon areaand the increase in transistor speed. Clearly, therefore, a balance mustbe struck between cost and capability when developing a lithographyprocess.

Optical lithography is a well-known photographic process by which aphotoresist layer comprising a polymer product deposited on a substrateis exposed (i.e., irradiated with UV light) and developed to form threedimensional relief images on the substrate. In general, the idealphotoresist image has the exact shape of the intended pattern in theplane of the substrate with vertical walls through the thickness of theresist. Thus, the final resist pattern is binary, with parts of thesubstrate covered with the resist while other parts are uncovered.Although the polymer product itself may be photoactive, generally aphotoresist contains one or more photoactive components in addition tothe polymer product. Upon exposure, the photoactive component acts tochange the physical or chemical characteristics of the photoresist.

As optical lithography is pushed to smaller dimensions, methods ofresolution enhancement, such as, for example, illumination modification,are considered necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of a contrast enhancing exposure system andmethod for use in semiconductor fabrication in accordance with anembodiment will be more clearly understood from the followingdescription taken in conjunction with the accompanying drawings in whichlike reference numerals designate similar or corresponding elements,regions, and portions, and in which:

FIGS. 1A-1C illustrate diffraction patterns resulting from use of maskscorresponding to patterns each having a different pitch.

FIG. 2 is a simplified diagram of a photolithography system in which anembodiment may be implemented.

FIG. 3 illustrates a three pore illumination pattern for implementing athree-pore illumination technique of one embodiment.

FIG. 4 illustrates a flowchart of a method for implementing a three-poreillumination technique in accordance with one embodiment for improvingdense orientation pattern contrast.

DETAILED DESCRIPTION

FIGS. 1A-1C each illustrates a diffraction pattern resulting fromexposure of a substrate to a light source via a mask corresponding to apattern having a particular pitch. In particular, FIG. 1A illustrates adiffraction pattern 10 resulting from exposure of a substrate through amask having a dense pitch (e.g., 220 nm). As shown in FIG. 1A,—1^(st)order diffraction is represented by an area 12, 1^(st) order diffractionis represented by an area 14, and zero order diffraction is representedby an area 16. An area of contrast useful information, which is definedas intensity adequate to provide sufficient contrast, is designated byellipses 18 a, 18 b, located near opposite edges of a numerical aperture(“NA”) 19 of a lens. FIG. 1B illustrates a diffraction pattern 20resulting from exposure of a substrate through a mask having asemi-dense pitch (e.g., 360 nm). As shown in FIG. 1B,—1^(st) orderdiffraction is represented by an area 22, 1^(st) order diffraction isrepresented by an area 24, and zero order diffraction is represented byan area 26. An area of contrast useful information is designated by anellipse 28 located at the center of an NA 29 of a lens. FIG. 1Cillustrates a diffraction pattern 30 resulting from exposure of asubstrate through a mask having an isolated pitch (e.g., 600 nm). Asshown in FIG. 1C,—1^(st) order diffraction is represented by an area 32,1^(st) order diffraction is represented by an area 34, and zero orderdiffraction is represented by an area 36. An area of contrast usefulinformation is designated by an ellipse 38 located at the center of anNA 39 of a lens.

Assuming that all of the lens NAs 19, 29, and 39 are identical, acomparison of FIGS. 1A, 1B, and 1C evinces the fact that, as the pitchdecreases (i.e., grows more dense), the 1^(st) order diffractionpatterns (both positive and negative) migrate toward the edge of thelens NA. In contrast, as the pitch decreases (i.e., grows less dense),the positive and negative 1^(st) order diffraction patterns migratetoward, and ultimately merge in, the center of the lens NA. It will berecognized that increasing the amount of 1^(st) order diffraction energythat is collected results in better contrast resolution at thephotoresist.

FIG. 2 is a simplified diagram of a photolithography system 200 in whichone or more of the embodiments may be implemented. As shown in FIG. 2,the system 200 includes a laser source 202, an illumination system 204,a reticle, or mask, 206, a projection lens 208, and a wafer stage 210 onwhich a wafer, or substrate, 212 to be imaged is supported. In oneembodiment, the illumination system 204 includes components suitable forshaping and conditioning the ultraviolet (“UV”) light from the lasersource 202 before it is shone through the reticle 206, which contains apattern to be imaged onto the wafer 212. Components of the illuminationsystem 204 may include, for example, an optical integrator and acondenser lens. It will be understood that the system 200 is providedfor purposes of example only and is not intended to limit application ofthe embodiments described herein to identical or similar systems.

In one embodiment, the illumination system 204 shapes the UV light toimprove the dense pattern contrast and reduce proximity effect. Inparticular, the system 204 utilizes a three-pore illumination shaper toaccomplish this result. The three-pore illumination shaper isillustrated in FIG. 3 and designated by a reference numeral 300. Asshown in FIG. 3, the shaper 300 includes three pores 302, 304, and 304.The shaper 300 enables isolated feature contrast to be obtained via thecentral pore 302, while the pores 304, which together comprise dipoleillumination, improve dense pitch contrast by increasing the amount offirst order diffraction energy that will be captured.

FIG. 4 is a flowchart illustrating a method of performing a contrastenhancing exposure method according to one embodiment. In step 400, apattern to be formed on a substrate is divided into two componentpatterns. Details regarding the manner in which this step may beaccomplished are provided in U.S. patent application Ser. No.11/677,879, entitled “Contrast Enhancing Exposure System and Method foruse in Semiconductor Fabrication,” which is assigned to the assignee ofthe present application and hereby incorporated by reference in itsentirety. As indicated in that disclosure, division of a pattern intotwo component patterns may be performed in a number of manners; however,the guiding principle to be used in determining how to divide thepattern is that the goal is to maximize the pitch (i.e., hole plusspace) in one direction (i.e., x or y direction) across the pattern. Instep 422, a mask is created from each of the component patterns. In step424, a photoresist layer of a substrate, or wafer, on which the patternis to be formed is exposed using a first one of the masks using asystem, such as the system 200 (FIG. 2) that employs an embodiment ofthe three-pore illumination technique described herein. In step 426, thephotoresist layer is exposed to the second one of the masks using asystem, such as the system 200 (FIG. 2) that employs an embodiment ofthe three-pore illumination technique described herein. In step 428, thesubstrate is developed, at which point other process steps (e.g.,etching, implantation, resist stripping) are performed as necessary tocomplete the fabrication process.

It will be recognized that it is not necessary to divide the patterninto two component patterns; however, doing so enables improved contrastinformation to be captured in both x- and y-directions. Specifically,the split pattern may be used to increase contrast in a first direction(e.g., the x-direction), while the three-pore illumination technique isemployed simultaneously to increase contrast in the other direction(e.g., the y-direction).

One embodiment is a photolithography apparatus comprising anillumination system for conditioning light from a light source, theillumination system producing a three-pore illumination pattern; areticle comprising at least a portion of a pattern to be imaged onto asubstrate, wherein the three-pore illumination pattern produced by theillumination system is projected through the reticle; and a projectionlens disposed between the reticle and the substrate.

Another embodiment comprises a photolithography apparatus comprisingmeans for providing ultra-violet (“UV”) light; means for conditioninglight the UV light and producing a three-pore illumination pattern;reticle means comprising at least a portion of a pattern to be imagedonto a substrate, wherein the three-pore illumination pattern isprojected through the reticle means; and lens means disposed between thereticle and the substrate.

Yet another embodiment is a method of forming a pattern on a substrate.The method comprises conditioning light from an ultraviolet light sourceto produce a three-pore illumination pattern; and projecting thethree-pore illumination pattern onto a substrate via a reticlecomprising at least a portion of a pattern to be imaged on thesubstrate.

While the preceding description shows and describes one or moreembodiments, it will be understood by those skilled in the art thatvarious changes in form and detail may be made therein without departingfrom the spirit and scope of the present disclosure. Therefore, theclaims should be interpreted in a broad manner, consistent with thepresent disclosure.

What is claimed is:
 1. A photolithography apparatus comprising: anillumination system for conditioning radiation from a light source, theillumination system comprising a three-pore illumination shaper, whereinat least one of the three pores is defined by a first edge of the shaperextending along a first axis and an opposing second edge of the shaperextending along a second axis, the first edge being connected to thesecond edge by a first plurality of edges of the shaper extending alongthe first axis and a second plurality of edges of the shaper extendingalong the second axis, the first axis being substantially perpendicularto the second axis; a reticle comprising at least a portion of a patternto be imaged onto a substrate, wherein a three-pore illumination patternprovided by the illumination system is projected through the reticle;and a projection lens disposed between the reticle and the substrate. 2.The apparatus of claim 1 wherein the illumination system furthercomprises an optical integrator and a condenser lens.
 3. The apparatusof claim 1 wherein the light source comprises a laser.
 4. The apparatusof claim 1 wherein the three-pore illumination shaper forms a pattern tobe imaged on the substrate that includes a high-density pattern.
 5. Theapparatus of claim 1 wherein the three pores includes a central pore forfacilitating capture of isolated features of the pattern to be imaged onthe substrate.
 6. The apparatus of claim 5 wherein the three poresincludes a pair of pores disposed on opposite sides of the central porefor facilitating capture of dense pitch features of the pattern to beimaged on the substrate.
 7. The apparatus of claim 6 wherein the pair ofpores are positioned so as to maximize the first order diffractionenergy captured during exposure.
 8. The method of claim 1 wherein the UVlight source comprises a laser.
 9. A method of forming a pattern on asubstrate, the method comprising: shaping radiation from an ultravioletlight source to provide a three-pore illumination pattern; andprojecting the three-pore illumination pattern onto a substrate via areticle comprising at least a portion of a pattern to be imaged on thesubstrate, wherein shaping radiation from the ultraviolet light sourceto provide the three-pore illumination pattern includes using athree-pore illumination shaper, and wherein at least one of the threepores is defined by a first edge of the shaper extending along a firstaxis and an opposing second edge of the shaper extending along a secondaxis, the first edge being connected to the second edge by a firstplurality of edges of the shaper extending along the first axis and asecond plurality of edges of the shaper extending along the second axis,the first axis being substantially perpendicular to the second axis. 10.The method of claim 9 wherein the pattern to be imaged on the substratecomprises a high-density pattern.
 11. The method of claim 9 wherein thethree-pore illumination pattern comprises a central pore forfacilitating capture of isolated features of the pattern to be imaged onthe substrate.
 12. The method of claim 11 wherein the three-poreillumination pattern comprises a pair of pores disposed on oppositesides of the central pore for facilitating capture of dense pitchfeatures of the pattern to be imaged on the substrate.
 13. The method ofclaim 12 wherein the pair of pores are positioned so as to maximize thefirst order diffraction energy captured during exposure of thesubstrate.
 14. A photolithography apparatus comprising: a mechanism forsecuring a substrate; a radiation source; a mechanism for securing areticle including a pattern; a projection lens disposed between thereticle and the substrate; and a multi-pore illumination device disposedbetween the radiation source and the substrate, wherein a first pore ofthe multi-pore illumination device enhances contrast of an isolatedfeature of the pattern, and a second pore of the multi-pore illuminationdevice enhances contrast of a dense feature of the pattern, the secondpore defined by a first edge of the multi-pore illumination deviceextending along a first axis and an opposing second edge of themulti-pore illumination device extending along a second axis, the firstedge being connected to the second edge by a first plurality of edges ofthe multi-pore illumination device extending along the first axis and asecond plurality of edges of the multi-pore illumination deviceextending along the second axis, the first axis being substantiallyperpendicular to the second axis.
 15. The apparatus of claim 14 whereinthe multi-pore illumination device is a three-pore shaper and the firstpore is centrally located relative to the other two pores.
 16. Theapparatus of claim 14 wherein the second pore works with a third pore ofthe three-pore shaper to enhance contrast of the dense feature andwherein the second and third pores are arranged on opposite sides of thefirst pore.
 17. The apparatus of claim 16 wherein the second and thirdpores are positioned so as to maximize the first order diffractionenergy captured during exposure.
 18. The apparatus of claim 14 whereinthe radiation source comprises a UV radiation source.
 19. The apparatusof claim 14 wherein the radiation source comprises a laser.